Answer this question truthfully
### Question: What are the causes of Klinefelter's syndrome?
### Response: Humans have 46 chromosomes. Chromosomes contain all of your genes and DNA, the building blocks of the body. The two sex chromosomes determine if you become a boy or a girl. Females normally have two of the same sex chromosomes, written as XX. Males normally have an X and a Y chromosome (written as XY).
Klinefelter's syndrome is one of a group of sex chromosome problems. It results in males who have at least one extra X chromosome. Usually, this occurs due to one extra X (written as XXY).
Klinefelter's syndrome is found in about 1 out of every 500 - 1,000 newborn males. Women who have pregnancies after age 35 are slightly more likely to have a boy with this syndrome than younger women.